This invention deals with development of an improved resin glass or ceramic composite system which has wide application and may be used for dental restorative filling materials for teeth and biomedical bone cement. It will be appreciated by one skilled in the art that modern ‘dental composite’ materials are a blend of glass and/or ceramic particles dispersed in a polymerizable synthetic organic resin. The polymer materials are blended together with the finely divided inorganic material such as a barium aluminosilicate or zirconium silicate glass or other glass ceramic compositions having an effective amount of radiopacifying agent that renders the resultant glass radiopaque to X-rays. Such dental restorative composite materials comprised of a blend of liquid polymerizable organic binder and a solid inorganic filler are known to the prior art. Such compositions are described in general terms for example in U.S. Pat. No. 3,066,112. The full potential application in dentistry of glass and glass/ceramic/resin composite biomaterials has not yet been achieved because the current composite materials cannot completely withstand the aggressive environment of the oral cavity. Major shortcomings are low fracture toughness and the inability of the composite materials to resist abrasion and wear in the mouth.
The dental restorative composite materials using the improved filler particles of this invention may be prepared according to known methods of the prior art such as employed in U.S. Pat. No. 3,066,112 which is hereby incorporated by reference for such disclosure. The improved composite restorative system having a tooth-like colour can be used to replace the conventional amalgam or gold dental fillings. Materials such as amalgam suffer from uncertainty as to the biological effect of the introduction of mercury into the oral cavity over long periods of time. In addition the metallic hue of amalgam restorations is not aesthetic.
Currently dental composite systems suffer from lack of sufficient adhesion being established between the inorganic (glass or ceramic) filler and the resin matrix. The modulus of elasticity of a composite material will show the effectiveness of the stress/strain transfer from matrix to the filler particles. The modulus of elasticity and Poisson's ratio of dental restorative materials are also regarded as important fundamental properties, because a material with a low elastic modulus will more readily elastically deform under a given masticatory functional force. Excessive elastic deformation of the restorative material under functional stress may result in catastrophic fracture of surrounding brittle tooth enamel structure, or alternatively increased microleakage may result. The increased use of polymer/glass composite systems as posterior restoratives (in back ‘molar’ grinding teeth) which are subjected to much higher levels of force than anterior restorations, might suggest the use of materials with a higher modulus of elasticity and fracture toughness in order to minimize the risk of cusp fractures. A dental restorative composite material with a higher modulus of elasticity and fracture toughness will be able to provide support at the interface with tooth enamel to protect the enamel rods at the margin from fracturing. Excessive wear of the restoration due to loss of filler particles (pull-out) followed by easier wearing away of the softer resin matrix is another problem in such situations.
A major limitation of the current dental composite materials is the relatively low fracture toughness. Fracture toughness is the energy absorbed by the material in resisting crack propagation. Dental restorative composite materials exhibiting higher fracture toughness values will have a better resistance to fracture and functional wear.